Comparing Terrestrial Laser Scanning (TLS) and Wearable Laser Scanning (WLS) for Individual Tree Modeling at Plot Level

Carlos Cabo,Susana Del Pozo,Celestino Ordóñez,Diego González-Aguilera,Pablo Rodríguez-Gonzálvez

doi:10.3390/rs10040540

Abstract

This study presents a comparison between the use of wearable laser scanning (WLS) and terrestrial laser scanning (TLS) devices for automatic tree detection with an estimation of two dendrometric variables: diameter at breast height (DBH) and total tree height (TH). Operative processes for data collection and automatic forest inventory are described in detail. The approach used is based on the clustering of points belonging to each individual tree, the isolation of the trunks, the iterative fitting of circles for the DBH calculation and the computation of the TH of each tree. TLS and WLS point clouds were compared by the statistical analysis of both estimated forest dendrometric parameters and the possible presence of bias. Results show that the apparent differences in point density and relative precision between both 3D forest models do not affect tree detection and DBH estimation. Nevertheless, tree height estimation using WLS appears to be affected by the limited scanning range of the WLS used in this study. TH estimations for trees below a certain height are equivalent using WLS or TLS, whereas TH of taller trees is clearly underestimated using WLS.

Highlights

Forest inventory is necessary to estimate the forest resources in a region or even a country and to plan their maintenance and efficient exploitation
A final 3D model of 54 million points for wearable laser scanning (WLS) data collection was obtained against the 70 million point cloud for the terrestrial laser scanning (TLS) data collection
The diameter at breast height (DBH) and tree height (TH) estimations were evaluated by comparing the results from WLS and TLS point clouds

Summary

Introduction

Forest inventory is necessary to estimate the forest resources in a region or even a country and to plan their maintenance and efficient exploitation. Forest inventory can be achieved using airborne laser scanning (ALS) data combined with field sampling. On a smaller scale, where more accurate and detailed information is required, data has to be collected at plot level or even at individual tree level. In this last case, traditional methods that use calipers and hypsometers are still normally used [19]. Despite the advantages of TLS for precise forest inventory, the time spent on data collection, due to its static nature, and the point cloud processing that is required mean that this technology has not been introduced yet among forest technicians [30]. The emergence of the wearable laser scanner (WLS) with real-time registering can substantially reduce these drawbacks

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Conclusion